Appendix A: Methodology for the 2007 General Aviation
and Part 135 Activity Survey
APPENDIX A
METHODOLOGY FOR THE 2007 GENERAL AVIATION
AND PART 135 ACTIVITY SURVEY
Purpose of Survey
The purpose of the General Aviation and Part 135 Activity (GA) Survey is to provide the Federal Aviation Administration (FAA) with information on general aviation and on-demand Part 135 aircraft activity. The information obtained from the survey enables the FAA to monitor the general aviation fleet so that it can anticipate and meet demand for National Airspace System (NAS) facilities and services, assess the impact of regulatory changes on the fleet, and implement measures to assure the safe operation of all aircraft in the NAS. The data collected are also used by other government agencies, the general aviation industry, trade associations, and private businesses to pinpoint safety problems and to form the basis for critical research and analysis of general aviation issues.
Background and History
Prior to the first implementation of the annual GA Survey in 1978, the FAA used the Aircraft Registration Eligibility, Identification, and Activity Report (AC Form 8050-73) to collect data on general aviation activity. The form was sent annually to all owners of civil aircraft in the United States and served two purposes: (1) Part 1 was the mandatory aircraft registration revalidation form, and (2) Part 2 was voluntary and applied to general aviation aircraft only, asking questions on the owner-discretionary characteristics of the aircraft such as flight hours, avionics equipment, base location, and use. The FAA used this information to estimate aircraft activity.
In 1978, the FAA replaced AC Form 8050-73 with a new system. Part 1 was replaced by a triennial registration program. In January 1978, the FAA implemented a new procedure, known as triennial revalidation, for maintaining its master file. Instead of requiring all aircraft owners to revalidate and update their aircraft registration annually, the FAA only required revalidation for those aircraft owners who had not contacted the FAA Registry for three years. This less frequent updating of the master file affected its accuracy and representativeness:
1.The accuracy of current owners and their addresses deteriorated.
2.The master file combined a residue of aircraft, which under the old revalidation system would have been reregistered and purged from the file, but now remain under the new system.
Part 2 of AC Form 8050-73 was replaced by the General Aviation Activity Survey. Conducted annually, the survey was based on a statistically selected sample of aircraft, and it requested the same type of information as Part 2 of AC Form 8050-73. The first survey took place in 1978 and collected data on the 1977 general aviation fleet.
In 1993, the name of the survey was changed to the General Aviation and Air Taxi Activity Survey to reflect that the survey included air taxi (that is, on-demand Part 135) aircraft. Starting in 1999, the avionics section, which had been included only every other year, was asked every year. As a result, the survey’s name was changed to the General Aviation and Air Taxi Activity and Avionics Survey. In 2006, “Part 135” replaced the term “Air Taxi” in the survey title, the word “Avionics” was removed (though avionics data were still collected annually), and the survey was named the General Aviation and Part 135 Activity Survey. This is the name under which the 2007 survey was conducted.
The GA Survey has undergone periodic revisions to content, implementation, and definition of the GA population in order to remain current with regulations, activity patterns, and general aviation community. The table below summarizes changes in survey content.
Year / Description of change to survey content1993 / Added sightseeing and external load to use categories
1996 / Added public use (i.e., flights for the purpose of fulfilling a government function) to use categories
1999 / Significant re-design of the entire survey form to reduce item non-response, add new content, and be compatible with optical scanning
Added air medical services to use categories
Discontinued the use of a catch-all ‘other’ category as used in previous years
Began collecting avionics data every year, rather than every other year
2000 / Public use asked as a separate question, independent of other use categories (e.g., personal/recreation, business transportation), because it was not mutually exclusive with respect to other flight activity
2002 / Use categories refined to be mutually exclusive and exhaustive and match definitions used by NTSB for accident reporting
2004 / Air medical services was divided into two separate types to capture air medical flights under Part 135 and air medical flights not covered by Part 135
A more clearly defined ‘other’ category was reintroduced
2005 / Fractional ownership question was changed from yes/no to a percentage
Reduced the number of fuel type response categories by removing obsolete options
Added question asking for average fuel consumption (in gallons per hour)
Revised avionics page by adding and rearranging items
2007 / Location of aircraft was revised to askthe state or territory in which the aircraft was “primarily flown” rather than where it was "based”
Percentage of hours flown in Alaska was added
Questions on percentage of hours flown under different flight plans, flight conditions, and day/night were revised into a single tabular format
Number of types of landing gear systems was expanded
Ice protection equipment was revised and prohibition from flight in icing conditions was added
Avionics equipage was significantly revised to reflect changes in technology
The table below summarizes changes in survey implementation.
Year / Description of change to survey implementation1999 / Non-respondent telephone survey conducted to adjust active aircraft and hours flown estimates[1]
2000 / Discontinued non-respondent telephone survey because of the variability of telephone non-respondent factors
Added Internet response option
2003 / Added a reminder/thank-you postcard between the first and second mailings
2004 / Introduced “multiple aircraft” summary form to allow owners/operators of multiple aircraft to report aggregate data for their entire fleet on a single form
Phone calls placed by PA and aviation associations to encourage participation by large fleet operators
The table below summarizes changes to the definition of the general aviation population and sample design.
Year / Description of change to definition of the GA population and sample design1993 / Number of aircraft types classified by the sample was expanded from 13 to 19
1999 / Sample design revised to stratify by aircraft type (19 categories) and FAA region (9 categories)[2]
2003 / Aircraft with known incorrect addresses and identified as “Postmaster Return” status on the Registry were retained in the definition of the survey population and were eligible for selection into the survey sample
2004 / Aircraft reported as “registration pending” or sold (if sold status less than 5 years) on the Registry were retained in the definition of the survey population and were eligible for selection into the survey sample
Sample design revised to stratify by aircraft type (19 categories), FAA region (9 categories), and whether or not the aircraft is owned by an entity certified to fly Part 135 (2 categories)
Introduced 100% sample of the following groups: turbine aircraft, rotorcraft, on-demand Part 135 aircraft, and Alaska-based aircraft
2005 / Sample design and reporting revised by introducing Light-sport aircraft as a 20th aircraft type sampled at 100%
2006 / Sample design simplified by reducing the number of aircraft types to 14 (removed distinctions based on number of seats and eliminated “Other” subcategories of Piston, Turboprop, and Turbojet aircraft)[3]
Sample design included 100% sample of aircraft manufactured in the past five years
The 2007 statistics in this report were derived from the thirtieth GA Survey, which was implemented in 2008.
Improvements to the 2007 Survey
As part of ongoing efforts to improve the survey data, five key changes were made to the 2007 survey:
- The field period opened on March 10, 2008, which matches the fielding date of the 2006 GA Survey (March 9, 2007). For two consecutive years, data collection began at the earliest date since the large-scale survey re-design in 1999.
- To obtain better information on the geographic distribution of aircraft activity, a new question on percentage of total hours flown in Alaskawas asked and wording was revised to identify where aircraft were primarily flown rather than “based.”
- To gather more accurate data on flight activity under different conditions, questions about flight plans, flight conditions, and day/night flying were revised to minimize complexity and respondent burden.
- To improve data on measures to improve the safe operation of aircraft under adverse conditions, questions on ice protection equipment and prohibition of flight under icing conditions were added.
- To remain current with technological advances, the avionics section was revised. Many new or more precisely worded items were added, several items were deleted, and material was rearranged to reflect more logical groupings.
Each of these improvements is discussed in subsequent sections of this Appendix.
Survey Population and Survey Sample
The survey population for the 2007 General Aviation and Part 135 Activity Survey includes all civil aircraft registered with the FAA that are based in the US or US territories and that were in existence and potentially active between January 1 and December 31, 2007.[4] This includes aircraft operating under:
- Part 91: General operating and flight rules.
- Part 125: Certification and operations: Airplanes having a seating capacity of 20 or more passengers or a maximum payload capacity of 6,000 pounds or more (but not for hire).
- Part 133: Rotorcraft external load operations.
- Part 135: On-demand (air taxi) and commuter operations not covered by Part 121.
- Part 137: Agricultural aircraft operations.
Aircraft operating under Part 121 as defined in Part 119 are excluded from the survey population. Foreign air carriers, which operate under Part 129, are also not part of the survey population. Civil aircraft that are known not to be potentially active during the survey year are also excluded from the population – i.e., aircraft displayed in museums, aircraft destroyed prior to January 1, 2007.
The Aircraft Registration Master File, maintained by the FAA’s MikeMonroneyAeronauticalCenter in Oklahoma City, serves as the sample frame or list of cases from which a sample of civil aircraft is selected. The Registration Master File (“Registry”) is the official record of registered civil aircraft in the United States. For the purpose of defining the 2007 survey population, we used the Registry’s list of aircraft as of December 31, 2007.
The Registry, like all sample frames, is an imperfect representation of the survey population. While it may exclude a very small number of aircraft that operate under the FAA regulations governing the operation of general aviation and on-demand Part 135 aircraft, it also includes aircraft that are not part of the survey population. Prior to sample selection, several steps are taken to remove ineligible aircraft from the sample frame. Specifically, this includes removing the following:
- Aircraft missing key identifiers that are necessary for classification or merging with other data sources (e.g., N-number, serial number, make/model information)
- Aircraft whose registration has been cancelled or revoked
- Aircraft based in Europe or registered to a foreign company that have not returned flight hour reports
- Aircraft that operate under Part 121
- Aircraft destroyed or moved to museums prior to January 1, 2007
- Aircraft reported sold before 2002 (5 years prior to survey year)[5]
- Aircraft that are flagged Postmaster Return (known to have incorrect address information) since before 1997 (10 years prior to survey year)
- Aircraft that are missing information on the registrant’s name (i.e., the field is blank) (Aircraft for which the registrant is listed as “Pending” are retained in the survey population[6])
- Aircraft that lack information necessary to execute the sample design (i.e., aircraft type, FAA region)
The Registry included 373,366aircraft as of December 31, 2007. This represents anincrease of 2.6 percent over the Registry file from 2006 (363,977 records). This increase is more than 1 percentage point larger than previous years[7] and largely reflects an influx of Light-sport aircraft. Large numbers of previously existing aircraft that flew under exemptions as Ultra-light aircraft could register as Experimental Light-sport until January 31, 2008. New rules governing the operation of Ultra-light aircraft would make the operation of these aircraft illegal after that date.
After excluding the aircraft described in the bulleted list above, 311,288 records remain. This represents 83.4 percent of the original Registry as of December 31, 2007, a percentage that is similar to previous years. The 2007 survey population of 311,288 represents an increase of 2.8 percent from 2006 (302,832). Again, this is a larger increase than previous years (more than 1 percentage point) due primarily to the registration of aircraft as Light-sport prior to the January 31, 2008 deadline for registering exempted Ultra-lights.
The 2007 GA Survey Sample
The 2007 survey sample design is unchanged from 2006.[8]The survey sample is stratified by aircraft type (14), FAA region in which the aircraft is registered (9), whether the aircraft operates under a Part 135 certificate (2), and whether the aircraft was manufactured in the past 5 years (2). Aircraft operated under a Part 135 certificate were identified using the FAA’s Operations Specifications Subsystem (OPSS) database that was merged with the Registry by N-number. The four stratifying variables yield a matrix of 504 cells.
Although aircraft types are reduced to 14 for the purpose of sampling, statistical estimates are reported for 17 aircraft types. The sample design retains distinctions by engine and major aircraft type but size differences (as defined by number of seats) within major aircraft types are collapsed. Charts A.1 and A.2 list the aircraft types that are used for sampling and how the more detailed set of types, for which statistical estimates are presented, map to those used for sampling.
Chart A.1 also shows the elimination of three “Other” categories that was initiated with the 2006 GA Survey. Improvements in the Registry over the years have left relatively few aircraft assigned to three residual categories: Fixed Wing Piston – Other, Fixed Wing Turboprop – Other, and Fixed Wing Turbojet – Other. Because these categories are relatively small and unable to support reliable statistical estimates, the aircraft are reassigned to the modal category in the corresponding larger group.
Chart A.1
Aircraft Types Used for Reporting
2005 GA Survey and Earlier 2006 GA Survey and Later
Chart A.2
Aircraft Types Used for Sample Design
2005 GA Survey and Earlier 2006 GA Survey and Later
The 2007 survey sample included several types of aircraft that were sampled at a rate of 1.0 (i.e., 100 percent sample). Because of the FAA’s interest in better understanding the operation of these aircraft, all such aircraft listed in the Registry were included in the survey sample to ensure a sufficient number of survey completes to support analysis and provide more precise estimates of fleet size and aircraft activity. These include:
- 100 percent sample of turbine aircraft (turboprops and turbojets)
- 100 percent sample of rotorcraft
- 100 percent sample of aircraft operating on-demand Part 135 (or, informally “Air Taxi” aircraft)
- 100 percent sample of aircraft based in Alaska[9]
- 100 percent of Light-sport aircraft
- 100 percent sample of aircraft manufactured within the past 5 years (since 2002 inclusive)
Since 2004, the survey design has included the first four 100 percent samples listed above. In 2005, we added the 100 percent sample of Light-sport aircraft. In 2006, we added the 100 percent sample of recently manufactured aircraft. Altogether, these aircraft contributed 68,934 observations to the 2007 survey sample. Other aircraft that are not part of a 100 percent sample are subject to selection based on sampling fractions defined for each cell in the sample design matrix. Average annual flight hours is the primary measure needed by the FAA to address survey goals. Sample fractions for each sample strata are defined to optimize sample size to obtain a desired level of precision for an estimate of flight activity. Data from the previous survey year on average hours flown, variability in hours flown by region and aircraft type, and response rates are used to set precision levels and identify the optimal sample size for each strata. Aircraft are randomly selected from each cell in the matrix, subject to the desired sample size. Strata that yield a very small sample size are examined and adjusted to include all observations in the strata if necessary. In 2007, an additional 15,636 aircraft were sampled at a rate of less than 1.0. The number of aircraft sampled at a rate of less than 1.0 is 63 percent smaller than the 2006 survey when 25,494 such aircraft were included in the sample. The large increase in number of aircraft captured by the 100 percent samples made it necessary to sample other aircraft at lower rates due to constraints on total sample size. The total sample for the 2007 GA Survey included 84,570 aircraft. Table A.1 shows the distribution of aircraft in the survey population and survey sample by aircraft type.
Table A.1: Survey Sample and Population Figures by Aircraft Type
Aircraft Type / Population / Sample Size / Sample as Percent of PopulationFixed Wing - Piston / 215,396 / 22,224 / 10.3
1 engine, 1-3 seats / 63,492 / 5,164 / 8.1
1 engine, 4+ seats / 128,808 / 13,700 / 10.6
2 engines, 1-6 seats / 15,566 / 1,826 / 11.7
2 engines, 7+ seats / 7,530 / 1,534 / 20.4
Fixed Wing - Turboprop / 10,556 / 10,556 / 100.0
1 engine / 4,462 / 4,462 / 100.0
2 engines, 1-12 seats / 4,912 / 4,912 / 100.0
2 engines, 13+ seats / 1,182 / 1,182 / 100.0
Fixed Wing - Turbojet / 11,894 / 11,894 / 100.0
2 engines / 11,894 / 11,894 / 100.0
Rotorcraft / 12,514 / 12,514 / 100.0
Piston / 4,439 / 4,439 / 100.0
Turbine: 1 engine / 6,561 / 6,561 / 100.0
Turbine: Multi-engine / 1,514 / 1,514 / 100.0
Other Aircraft / 10,317 / 5,238 / 50.8
Glider / 3,204 / 2,395 / 74.8
Lighter-than-air / 7,113 / 2,843 / 40.0
Experimental / 42,154 / 13,687 / 32.5
Amateur / 36.687 / 9,582 / 26.1
Exhibition / 3,184 / 1,917 / 60.2
Experimental: Other / 2,283 / 2,188 / 95.8
Light-sport / 8,457 / 8,457 / 100.0
Total / 311,288 / 84,570 / 27.2
Weighting the Survey Data